The present invention relates to a semiconductor device including a ferroelectric film formed by CVD and a method for fabricating the same.
In recent years, further miniaturization has been demanded in the field of ferroelectric memory. With a known method in which a ferroelectric film is formed by coating, however, a ferroelectric film can be formed only on a flat underlying layer. Therefore, with the known method, there is a limitation in terms of how much the size of memory cells can be reduced. Then, to reduce the size of memory cells, a method in which a ferroelectric film is formed using thermal CVD allowing film formation on an underlying layer having level differences has been proposed.
Hereinafter, a known method for fabricating a semiconductor device will be described with reference to FIG. 15.
FIG. 15 is a flow chart showing the known method for fabricating a semiconductor device.
A lamination film of indium oxide, iridium and titanium aluminum nitride is formed on a semiconductor substrate in advance, and then a silicon oxide film is formed over the semiconductor substrate so as to cover the lamination film. Furthermore, a recess portion is formed in the silicon oxide film so that part of a surface of the lamination film is exposed through the recess portion (not shown).
Next, in Step S81, a lower electrode of a lamination film of platinum (Pt) and iridium oxide (IrOx) is formed along inner surfaces of the recess portion in the silicon oxide film by sputtering.
Next, in Step S82, the lower electrode formed in Step S81 is patterned using lithography and etching.
Next, in Step S83, CVD is performed at a temperature of 350° C. and a pressure of 1.33×102 Pa (1 Torr) and with a gas obtained by diluting ST-1 [Sr(Ta(OEt)5(OC2H4OMe))2] at a concentration of 0.1 mol % in ECH (ethylcyclohexane) flowing at a flow rate of 100×10−3 ml/min, a gas obtained by diluting Bi (MMP)3 at a concentration of 0.2 mol % in ECH (ethylcyclohexane) flowing at a flow rate of 200×10−3 ml/min, a gas obtained by diluting PET [Ta(OC2H5)5] at a concentration of 0.1 mol % in ECH (ethylcyclohexane) flowing at a flow rate of 100×10−3 ml/min, an oxygen (O2) gas flowing at a flow rate of 1000×10−3 ml/min, and an argon (Ar) gas flowing at a flow rate of 1900×10−3 ml/min so that these source gases are reacted with one another for about 30 minutes. Thus, an SBT (SrBi2Ta2O9) film to serve as a ferroelectric film is deposited so as to have a thickness of about 60 nm.
Next, in Step S84, a platinum film as an upper electrode is formed by sputtering on the SBT film formed in Step S83.
Next, in Step S85, the upper electrode formed in Step S86 is patterned using lithography and etching.
The known semiconductor device formed according to the above-described steps will be described with reference to FIG. 16.
As shown in FIG. 16, a lamination film of iridium oxide 103, iridium 102 and titanium aluminum nitride 101 is formed on a semiconductor substrate (not shown). On the semiconductor substrate, a silicon oxide film 104 is formed so as to cover the lamination film. The silicon oxide film 104 includes a recess portion 104a through which a surface of the lamination film is exposed.
Moreover, on the silicon oxide film 104 including the recess portion 104a, a lower electrode 105 of a lamination film of platinum and iridium oxide, an SBT film 106 as a ferroelectric film, and an upper electrode 107 of a platinum film are formed in this order from the bottom along inner surfaces of the recess portion 104a. 
Although, as a known example of the case where a ferroelectric film is formed on a flat underlying layer by coating, a method in which a ferroelectric film is formed so as to include multiple layers has been disclosed, for example, in Japanese Patent Publication No. 2964780, any method for solving the following problems to arise in the case where a ferroelectric film is formed using CVD has not been disclosed.
With the known method for fabricating a semiconductor device and the known semiconductor, the composition of an obtained ferroelectric film can not be uniform in the film thickness direction. If the composition of a ferroelectric film is non-uniform in the film thickness direction, excellent electric characteristics of a capacitor can not be achieved.